1. Technical Field
The disclosure relates to an organic light emitting display, and more particularly, to an organic light emitting display having threshold voltage compensation mechanism and driving method thereof.
2. Description of the Related Art
Because flat panel displays (FPDs) have advantages of thin appearance, low power consumption, and low radiation, various kinds of flat panel displays have been developed and widely applied in a variety of electronic products such as computer monitors, mobile phones, personal digital assistants (PDAs), or flat panel televisions. Among them, active matrix organic light emitting displays (AMOLEDs) have gained more and more attention due to further advantages of self-emitting light source, high brightness, high emission rate, high contrast, fast reaction, wide viewing angle, and extensive range of working temperature.
FIG. 1 is a structure diagram schematically showing a prior-art active matrix organic light emitting display 100. As shown in FIG. 1, the active matrix organic light emitting display 100 comprises a scan driving circuit 110, a data driving circuit 120, and a plurality of pixel units 150. Each pixel unit 150 includes an input transistor 151, a driving transistor 152, a storage capacitor 153, and an organic light emitting diode 154. The scan driving circuit 110 and the data driving circuit 120 are utilized for providing plural scan signals and plural data signals respectively. Each pixel unit 150 is employed to control a driving current Id based on corresponding scan and data signals, for controlling the light-emitting operation of one organic light emitting diode 154 disposed therein. However, in the operation of the active matrix organic light emitting display 100, the threshold voltage of the driving transistor 152 has en effect on the driving current Id, and therefore the threshold voltage variation of the driving transistors 152 in the pixel units 150 will cause pixel brightness distortion on the OLED screen, thereby degrading display quality. Besides, the voltage/current hysteresis effect of the driving transistor 152 is likely to incur image retention phenomenon. For instance, if two adjacent pixel units 150 are employed to illustrate a white-color grey level and a black-color grey level respectively in a first frame, and the control voltages Vctr of the two pixel units 150 are both set to one and the same voltage corresponding to a middle grey level between the white-color and black-color grey levels in a second frame following the first frame, the driving currents Id of the two pixel units 150 are then different due to the aforementioned hysteresis effect, which results in edge residual phenomenon.